1. Field of the Invention
The present invention relates to a flowmeter for detecting the flowrate in a pipe or tube and in particular to a T-shape vortex shedder which is optimized in shape for use as a flowmeter.
2. Description of the Prior Art
Vortex shedding meters are the most common used among fluid oscillatory type meters. A vortex flowmeter detects frequency of vortex shedding from a bluff body which, as learned from fluid dynamics, is linearly proportional to the fluid velocity under certain conditions. Relevant papers discussing this phenomenon can be found in: H. V. Magin, Tappi 58 65 (1975); D. J. Lomax, Control Instrument 7, 36 (1975); and T. J. S. Brain and R. W. W Scott, J.Phys. E 15, 967 (1982).
Conventional vortex flowmaters include a two dimensional bluff body accommodating a pressure sensor or a probe for detecting vortex shedding frequencies. If a bluff body is placed in a fluid flow, as shown in FIG. 1, under certain conditions, when the fluid flows over the upper and lower ends 1a and 1b of this bluff body 1, the fluid will separate at an upper front end 1a1 and a lower front end 1b1 of the bluff body 1 and produce vortex shedding in the downstream direction continuously and alternately. The shedding frequency is defined as the number of vortices developed in a certain time. Since vortex shedding produces a variation in fluid pressure, the vortex shedding frequency f can be determined by the variation of pressure, and then the fluid flowrate can be calculated according to the determined frequency f. The operating theories of such vortex shedding meters are further explained in U.S. Pat. No. 5,170,671, issued to Miau et al., the disclosure of which is incorporated herein by reference.
All current vortex flowmeters are designed on the above principle. However, in order to precisely determine a broad range of fluid flowrates, the design of the bluff body and the method of the measurement of frequency differ in many ways. The quality of a flowmeter mainly depends on the quality of the signals of the vortex shedding frequency. When the vortex shedding becomes steadier and the size of vortex becomes more definite, the quality of the signals of the vortex shedding frequency improves.